JPH0547901B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an optical disk device that records or reproduces information on or from a rotating disc-shaped record carrier using optical means. In contrast, move the light spot,
The present invention relates to a tracking control device that performs positioning or follows changes in track position.

In an optical disk device, a large number of approximately concentric information tracks are formed on an optical disk-shaped record carrier, and by tracing these information tracks with an optical head (more precisely, an optical spot), information can be recorded, Regeneration takes place.

In such a device, a light beam spot is precisely positioned at the center of the track and tracked to follow changes in the track position, or tracking control is used to accurately and quickly move the light beam spot from the currently tracing track to the target track. Is required. In general, a focusing lens that focuses the laser beam onto the surface of the record carrier is used to change the position of the optical spot in the disk radial direction (track lateral direction) in order to follow such changes in track position or move between tracks. This is done by moving the. However, if you move only the focusing lens without moving other optical components such as the laser light source and photodetector, the center of the focusing lens may shift from the optical axis center of the light beam from the laser light source or the center axis of the detection optical system. In addition to causing an offset in track position error detection, the convergence of the light beam spot deteriorates, and information recording and reproducing characteristics also deteriorate. Furthermore, due to the presence of a spring or the like that keeps the focusing lens at its central position, large displacements of the lens position result in an increase in the restoring force and a decrease in control characteristics.

In order to solve these difficulties, it is preferable not to move only the focusing lens, but also to move the other optical system, excluding the focusing lens, together with the focusing lens. A tracking control device configured in this manner is described, for example, in Japanese Patent Application No. 58-068627 entitled "Track Following Device in Optical Disk System".
is shown. In this example, in addition to the focusing lens,
A means for detecting the positional deviation of the focusing lens with respect to the reference position of the frame of the optical head equipped with a lens actuator, a laser light source light detector, a prism lens, etc. is provided, and the positional deviation of the focusing lens with respect to the optical head frame is eliminated. , the position of the optical head or focusing lens is controlled. With this configuration, when the focusing lens moves to move the optical spot, the deviation of the focusing lens position from the center of the laser optical axis of the optical head can be suppressed to a certain degree. However, while the focusing lens itself is extremely small and lightweight, the optical head as a whole has considerable size and weight. The frequency is low compared to the band, and with position control that only detects the positional deviation of the focusing lens and moves the optical head to reduce the deviation, when the focusing lens moves at high speed, the focusing lens and the optical It becomes difficult to keep the displacement of the head frame sufficiently small. For example, if the band of the servo loop that moves the optical head is 200Hz and the focusing lens moves at an acceleration of 2G, the positional deviation will be approximately
It becomes 15μm. This value is compared to the case where the optical head does not follow the focusing lens.
Although this is an extremely small value, it is considerably larger than the track pitch of an optical disk, which is 1.6 μm to 2.5 μm, and it cannot be said that positional deviation is sufficiently suppressed.

It is an object of the present invention to eliminate the problems in the conventional method and to provide a system that uses a focusing lens and an optical head when a light spot moves between tracks at high speed or when tracking a track position change with high speed and large amplitude. It is an object of the present invention to provide a tracking control device in which positional deviation with respect to a frame is suppressed to a small extent, and therefore, stable, high-speed, and highly accurate track access or track following operation can be performed.

According to the present invention, the positional deviation between the focusing lens and the optical head frame during the track following operation is suppressed to a small level, the convergence of the optical beam spot is increased, and the information recording and reproducing characteristics are not only improved, but also
It becomes easier to realize the track access operation of the optical beam spot by moving the focusing lens, which was difficult because the positional deviation between the lens and the optical head becomes too large.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the tracking control device of the present invention.

The semiconductor laser 5 is supplied with current from the laser drive circuit 20 and emits laser light.

The diverging laser beam emitted from the semiconductor laser 5 is converted into parallel light by the collimating lens 6.
The light passes through a polarizing beam splitter 7 and a quarter-wave plate 8 and enters a half mirror 9.

The half mirror 9 splits the incident laser beam and directs a part of it to the lens position detector 10 .

The remaining light beam that passes straight through the half mirror 9 is reflected by the reflecting mirror 11 and enters the focusing lens 3 with its optical path bent. The focusing lens 3 focuses the incident light beam to form a minute light beam spot on the surface of the record carrier 1.

The focusing lens 3, reflector 11 and half mirror 9 are mounted on a common arm 12 and moved together by a lens actuator 2. As a result, when the focusing lens 3 is moved in the radial direction (in the lateral direction in the figure) of the record carrier 1 by the lens actuator 2, the half mirror 9 moves together, and the laser beam incident on the lens position detector 10 Change the position of the axis center. Therefore, the lens position detector 1
0, the movement of the focusing lens 3 can be detected by detecting the lateral intensity difference of the incident light beam using a photodetector divided into two, for example.

The laser beam reflected from the surface of the record carrier 1 passes through the focusing lens 3, the reflecting mirror 11, and the half mirror 9 again, has its polarization angle rotated by the 1/4 wavelength plate 8, and is divided by the polarizing beam splitter 7. Then, the optical path is bent and the beam enters the track position deviation detector 4.

The track position deviation detector 4 detects the change in the intensity distribution of the reflected laser beam, the light intensity distribution of which is changed according to the track position information recorded on the surface of the record carrier 1, and detects the change in the intensity distribution of the reflected laser beam formed on the surface of the record carrier 1. A current corresponding to the positional deviation of the minute light beam spot with respect to the track center is output. The optical system forming the optical path from the semiconductor laser 5 to the focusing lens 3, the lens actuator 2, the lens position detector 10, and the track position deviation detector 4 are housed in one optical head frame 13 as shown in the figure. The optical head is incorporated into the optical head as a whole.

This optical head frame 13 (or optical head) is moved in the radial direction of the record carrier 1 by a head actuator 14 composed of a linear motor or the like.

That is, the focusing lens 3, the reflecting mirror 11, and the half mirror 9 are moved in the radial direction of the record carrier 1 by the lens actuator 2, but the remaining parts (including the lens actuator 2) constituting the optical head are moved by the lens actuator 2. are moved radially by head actuator 14. Therefore, when the lens actuator 2 and the head actuator 14 operate completely separately, the optical head frame 13 of the focusing lens 3
The position within the center will always deviate from the center position in its resting state. In order to avoid such a situation, it is necessary to move the optical head frame 13 in accordance with the movement of the focusing lens 3, or in other words, it is necessary to cause the movement of the lens actuator 2 and the movement of the head actuator 14 to move together. becomes.

In the apparatus of the present invention, the lens position detector 10 detects the positional deviation of the focusing lens 3 with respect to the optical head frame 13, and so as to reduce the deviation.
The movement of the head actuator 14 is controlled so that the focusing lens 3 and the optical head frame 13 move almost integrally.

The differential amplifier 21 receives the output current of the lens position detector 10 and outputs the optical head frame 1 of the focusing lens 3.
Lens position deviation signal 1 indicating position deviation with respect to 3
Outputs 01.

The lens position deviation signal 101 is input to the phase compensation filter 22, and after being phase compensated, it is sent to the drive amplifier 23.
Enter. The drive amplifier 23 receives the phase-compensated lens position deviation signal 101 and the lens drive current value signal 103, adds them together, amplifies them, and supplies a drive current 104 to the head actuator 14. The head actuator 14 generates a driving force proportional to the supplied current, and moves the optical head frame 13 (more precisely, the optical head) with an acceleration approximately proportional to the driving force. This constitutes a position servo loop in which the optical head frame 13 follows the movement of the focusing lens 3.

On the other hand, the positional deviation of the minute light beam spot formed on the surface of the record carrier 1 by the focusing lens 3 with respect to the information track is detected by the track position deviation detector 4.
causes a difference in the output current.

The differential amplifier 24 receives the output current of the track position deviation detector 4 and generates a track position deviation signal 102 indicating the position deviation of the optical spot with respect to the information track.
Output.

The track position deviation signal 102 is input to a phase compensation filter 25, and after being phase compensated, it is input to a mode changeover switch 26. Mode changeover switch 26
is the phase compensation filter 25 during track following operation.
The output is selected and passed, and is input to the drive amplifier 27.

The drive amplifier 27 amplifies the input signal and supplies a drive current 105 to the lens actuator 2. The lens actuator 2 generates a driving force proportional to the supplied current, and moves the focusing lens 3 (more precisely, all the parts attached to the arm 12) with an acceleration proportional to the driving force.

This constitutes a track following servo loop in which the focusing lens 3 moves so that the light beam spot accurately hits the information track position on the record carrier 1.

When performing a track access operation in which the light beam spot moves between tracks, the mode changeover switch 206 is switched by the mode changeover signal 106 output from the access control circuit 29.
A lens acceleration/deceleration signal 107 output from the access control circuit 29 is selected and input to the drive amplifier 27. The method for generating and supplying the acceleration/deceleration signal 107 when accessing the track of this optical spot is explained in detail in Japanese Patent Publication No. 1051/1988 ``Reading Apparatus for Disc-shaped Record Carrier'', so detailed explanation will not be given in this text. Omitted. The drive amplifier 27 supplies an acceleration/deceleration current corresponding to the lens acceleration/deceleration signal 107 to the lens actuator 2 to move the focusing lens 3 by a required distance.

The optical head frame 13 of the focusing lens 3 during both track following and track access operations.
The lens position detector 10 detects the positional deviation with respect to the lens frame 13, and the head actuator 14 moves the lens frame 13 so as to reduce the deviation.

However, whereas the lens actuator 2 only needs to move relatively small and lightweight parts, mainly the focusing lens 3, the head actuator 14
Since this moves the entire optical head, which is larger in weight and size than a focusing lens, mechanical resonance in the force transmission section occurs at a relatively low frequency. Therefore, the response frequency band of the optical head frame position servo loop from the lens position detector 10 to the head actuator 14 is lower than the response frequency band of the track following servo loop that moves only the focusing lens 3, and the lens position deviation signal is It is difficult for the optical head frame 13 to accurately follow the high-speed movement of the focusing lens 3 using only a basic position servo loop that amplifies the signal 101 and supplies it to the lens actuator 14.

Therefore, when the focusing lens 3 is following track position fluctuations with large amplitude and high frequency, or when the focusing lens 3 is moving at high speed due to the movement of the light spot between tracks, the focusing lens 3 The positional deviation between the optical head frame 13 and the optical head frame 13 becomes so large that it cannot be ignored, and there is a possibility that the recording and reproducing characteristics of information or the characteristics of detecting a track positional deviation will be deteriorated.

In the device of the present invention, the drive current 105 for accelerating and decelerating the lens actuator 2 is supplied to the current sense amplifier 2.
8, amplifies and converts the signal, inputs it to the drive amplifier 23 as a lens drive current value signal 103, and adds it to the output of the phase compensation filter 22. 13 is suppressed to a smaller extent. That is, the acceleration/deceleration generated by the lens actuator 2 depends on the drive current 105 supplied thereto.
Since it is proportional to the value of , the lens drive current value signal 10
3 and supplying a current proportional to the value to the head actuator 14, it is possible to generate an acceleration in the head actuator 14 that is approximately equal to the acceleration of the lens actuator 2. Therefore, the optical head frame 13 is the focusing lens 3.
Head actuator 1 for following the movement of
Most of the drive current 104 of No. 4 is generated by amplifying the lens drive current value signal 103,
The value remaining as the amount of positional deviation between the focusing lens 3 and the optical head frame 13 becomes extremely small. In order to effectively perform such a function, the gain A of the current sense amplifier 28 is preferably set as follows. The weight of the lens movable part including the focusing lens 3 moved by the lens actuator 2 is M ₁ ,
If the force constant of the lens actuator 2 is K _F1 , the acceleration α ₁ generated by the lens actuator 2 when the current I ₁ is supplied is α ₁ =K _F1 I ₁ /M ₁ .

On the other hand, the weight of the movable parts moved by the head actuator 14, including all internal parts of the optical head frame 13, is _M2 , and the head actuator 1
Assuming that the force constant of 4 is K _F2 , in order to generate the same acceleration as α ₁ of the lens actuator 2, a current of I ₂ =α ₁ M ₂ /K _F2 must be supplied.

Assuming that the gain of the drive amplifier 23 is G ₂ , in order to generate this current I ₂ , the input lens drive current value signal 103 value E ₁ = I ₂ /G ₂ = α ₁ M ₂ /K _F2 G ₂ = K _F1 M ₂ I ₁ /K _F2 M ₁ G ₂ . Therefore, if the gain A of the current sense amplifier 28 that converts the drive current value I ₁ of the lens actuator 2 to E ₁ is set to A=K _F1 M ₂ /K _F2 M ₁ G ₂ (V/A), good.

Note that even if the gain A of the current sense amplifier 28 deviates somewhat from the above value, the positional deviation between the focusing lens 3 and the head frame 13 can be compensated for by the current sense amplifier 28.
There is an effect of suppressing it to a smaller value than in the case without 8.

FIGS. 2A and 2B are diagrams showing examples of signal waveforms at various parts of the apparatus for explaining the operation of the apparatus shown in FIG. 1.

FIG. 2A shows signal waveforms of various parts during track following operation.

When the track position changes as shown by the solid line a, the focusing lens 3 follows this track position change by the action of the track following servo loop, and the light beam spot hitting the surface of the record carrier 1 is moved as shown by the broken line b.
As shown in , the movement is almost the same as the track position fluctuation.

At this time, the lens actuator drive motor 105
The value changes as shown by solid line C.

The optical head frame 13 is connected to a head actuator 14 so as to follow the movement of the focusing lens 3.
The lens drive current value signal 10
In the configuration in which only the lens position shift signal 101 is inputted to the drive amplifier 23 without using the lens position shift signal 3, the optical head frame 13 cannot accurately follow the movement of the focusing lens 3, and the movement of the focusing lens 3 and the optical head frame 13 is The positional deviation between them remains as a fairly large value as shown by the broken line α. On the other hand, if the configuration of the present invention is adopted in which the lens drive current value signal 103 is added to the input of the drive amplifier 23, the positional deviation between the focusing lens 3 and the optical head frame 13 (lens position deviation signal 101 ) can be suppressed to extremely small fluctuations.

FIG. 2B shows signal waveforms of various parts during the movement between tracks.

A focusing lens 3 is connected to a lens actuator 2 in order to move a light beam spot formed on the surface of the record carrier 1 from the current track to another track.
The optical head frame 13 is moved by the head actuator 14 so as to follow the movement of the focusing lens 3 when the optical head frame 13 is accelerated and decelerated by the focusing lens 3 and changes in speed as shown by the solid line f. However, in a configuration in which only the lens position deviation signal 101 is inputted to the drive amplifier 23 without using the lens drive current value signal 103, the speed of the optical head frame 13 is As shown by the broken line g, a deviation occurs between the movement f and the movement f of the focusing lens 3. At this time, the positional deviation between the focusing lens 3 and the optical head frame 13 becomes considerably large as shown by the broken line j. On the other hand, the lens actuator drive current 105, which changes as shown by the solid line h, is detected by the current sense amplifier 28 and added to the input of the drive amplifier 23 as the lens drive current value signal 103. The frame 13 follows the movement of the focusing lens 3 almost exactly, and the positional deviation between the focusing lens 3 and the optical head frame 13 is kept extremely small as shown by the solid line j.

Considering an ideal situation, by adding the lens drive current value signal 103 to the input of the drive amplifier 23, it is possible to reduce the variation amount of the lens position deviation signal 101 to almost 0, but in reality, Due to errors in amplifier gain settings, deviations in actuator characteristics, etc., the value of the lens position deviation signal 101 cannot be strictly set to 0. However, even if relatively coarse gain settings are made, the lens drive current value signal 103
It is easy to reduce the positional deviation between the focusing lens 3 and the optical head frame 13 to about 1/10 compared to the case where the optical head frame 13 is not used.

As described above, according to the present invention, whether a light spot is made to follow an information track with large positional fluctuations or a light spot is moved at high speed to another information track, a moving convergence beam is used to move the light spot. lenses and other optical systems,
The positional deviation with the optical head frame on which the detection system is mounted is kept extremely small, and a device that performs high-speed, stable, and highly accurate track access and highly accurate and stable track following operation can be realized. It is possible to improve recording and reproducing characteristics, shorten track access time, etc.

In this explanatory note, for convenience of explanation, only some examples of optical disk devices have been described. Of course, modifications can be made without departing from the spirit, and the scope of the present invention is not limited to the above examples.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the tracking control device of the present invention, FIG. 2A is a diagram showing signal waveforms of various parts of the device shown in FIG. FIG. 3 is a diagram showing signal waveforms of various parts of the device shown in the figure during inter-track movement operation. In the figure, 1 is a record carrier, 2 is a lens actuator, 3 is a focusing lens, 4 is a track position deviation detector, 5 is a semiconductor laser, 6 is a collimating lens,
7 is a polarizing beam splitter, 8 is a quarter wavelength plate,
9 is a half mirror, 10 is a lens position detector, 1
1 is a reflecting mirror, 12 is a support arm, 13 is an optical head frame, 14 is a head actuator, 20 is a laser drive circuit, 21 is a differential amplifier, 22 is a phase compensation filter, 23 is a drive amplifier, and 24 is a differential 25 is a phase compensation filter, 26 is a mode changeover switch, 27 is a drive amplifier, 28 is a current sense amplifier, and 29 is an access control circuit.

Claims (1)

[Claims] 1. In an optical disk device that reads or records information by focusing a light beam from a laser light source on a rotating disk-shaped record carrier to a minute spot, the minute light spot is moved in the radial direction of the record carrier. a lens actuator that moves a focusing lens that narrows down the laser beam in order to
a head actuator that moves the optical head, which integrates the focusing lens, lens actuator, laser light source, optical components for recording and reading information, and a photodetector, in the radial direction of the record carrier; a photodetector attached to the optical head to detect the positional deviation of the optical spot with respect to the information track on the record carrier; a position detector attached to the optical head to detect the positional deviation of the focusing lens with respect to the center of the laser beam; , means for detecting a current value supplied to the lens actuator, and by moving the focusing lens by the lens actuator, the minute light spot follows an information track on the record carrier. Alternatively, the light spot is moved between the information tracks, and the head actuator is supplied with a current corresponding to the positional deviation of the focusing lens with respect to the center of the laser beam, and a current value proportional to the current value supplied to the lens actuator. Tracking in an optical disk device, characterized in that by supplying an additional current, the movement of the optical head follows the movement of the focusing lens, and the positional deviation of the focusing lens with respect to the center of the laser beam is suppressed to a small value. Control device.